Effect of gamma radiation on geopolymerization and microstructure development of metakaolin-based geopolymer for Cesium and Strontium waste immobilization

This study examines the effect of gamma radiation on geopolymerization kinetics and early age microstructural development in metakaolin-based geopolymers incorporating simulated cesium (Cs) and strontium (Sr) radio¬ active waste. The effects of heat induced during gamma irradiation were decoupled from those of gamma ionizing radiation and assessed independently. Furthermore, a comparative analysis was conducted between the effects of gamma radiation from Co-60 source, commonly utilized in irradiation studies, and those from Cs-137 source associated with Cs- and Sr-containing waste. The results indicate that gamma radiation-induced heat only impacts the early reaction kinetics, without affecting the total 28-day degree of reaction. Co-60 irradiation does not interfere with the geopolymerization process, but Cs-137 exposure negatively affects the geopolymerization and subsequent formation of N–A–S–H gel. One of the evidences is the highest proportion of unreacted MK of 26.3 % with Cs-137 exposure compared to 18.6 % with Co-60 exposure at the same cumulative dose. This implies that the commonly used Co-60-based irradiation underestimates the radiation impact in real-world Cs/Sr waste immobilization. In addition, N–A–S–H gel exhibited radiation stability as indicated by FTIR, TGA, quantitative XRD, NMR, and SEM analysis. Based on the results, metakaolin-based geopolymers are promising as inexpensive alternatives to vitrification for the immobilization of Cs-137 and Sr-90-containing waste. Future studies using insitu irradiation are needed to assess the effect of gamma radiation on the entire geopolymerization process.